Process of thermographic copying



Aug. H, 1970 M. N. VRANCKEN ET AL 3523,79i

PROCESS OF THERMOGRAPHIC COPYING Filed June 22, 1966 2 Sheets-Sheet 1 i Q Q 2 i INVENTORS MARCEL NICOLAS VRANCKEN ALEXANDER RIEBEL WATSON,COLE, GR/NDLE & WATSON ATTORNEYS g 1970 M. N. VRANCKEN ET AL 3,523,791

PROCESS OF THERMOGRAPHIC COPYING Filed June 22. 1966 2 Sheets-Sheet a l i j 7% INVENTORS MARCEL NICOLAS VRANCKEN ALEXANDER R/EBEL WATSON, COLE, GRINDLE & WA TSON ATTORNEYS United States Patent US. C]. 96-28 14 Claims The present invention relates to a method for recording and reproducing information by means of image-Wise reflected electromagnetic radiation.

In accordance with the present invention a recording material, which contains a recording layer mainly consisting of gelatin and containing in heat-conducting relationship therewith substances that absorb visible light and convert it into heat, is reflectographically exposed to an original as defined hereinafter, the exposure being of short duration and of such high intensity that an image or record is formed as an increase in the rate of swelling and dissolving of the gelatin in water.

The original is one containing image areas on an imagebackground that reflect(s) visible light or is a transparency or stencil that has electromagnetic radiation absorbing areas and that is held during the exposure with its backside in contact or in proximity of a material reflecting visible light. Originals wherein both image areas and background reflect Visible light but to sufliciently different extents for obtaining a practically useful image differentiation are not excluded.

For reproduction purposes use is made of the imagewise differentiation in swelling degree of the layer mainly consisting of gelatin, called hereinafter the gelatin layer. The gelatin layer, which after exposure is moistened with water or an aqueous liquid composition, shows a gelatin relief image, which may be used for producing a printing master. According to one technique, in the case unhardened gelatin is used, a gelatin stratum of the swollen areas corresponding with the heat pattern can be transferred to a receiving sheet. If the gelatin is hardened to a certain degree only moisture absorbed in the swollen portions is transferred.

It is emphasized that during the exposure the heat applied in the gelatin-containing recording layer may only result from the light converted into heat in said substances and that no heat absorbed by the image markings of the original may be transferred to the said layer in such an amount that a differentiation in solubility and swellability in water is obtained.

In that connection it has been observed that when applying an exposure of short duration (exposure time preferably not higher than second) the gelatin-containing recording layer may stand in contact with the lightabsorbing markings of the original during that exposure. Although the said markings are thus in some degree in heat-conducting relationship with the gelatin layer, they do not elfectively heat the gelatin. So, it is apparent that the recording method is not dependent in any way on the extent of contact between the original to be recorded and the gelatin-containing layer during exposure.

According to an embodiment, wherein heat transfer during the exposure from the image-markings of the original to the recording layer is practically completely excluded, between the recording layer and the said markings a poorly heat-conductive material, e.g. a paper support or resin layer or support is arranged.

In the applied reflectographic exposure technique said layer or support of course has to be transparent for the copying light.

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An increase in temperature of the gelatin of between 50 and 200 C. causes a substantial increase in the tendency of the gelatin to swell in water. Before being heated the gelatin exists in gel state whereas by heating the gelatin structure is changed in a structure similar to that of a sol-dried gelatin, i.e. a gelatin dried at a temperature higher than 35 -40 C.

The differential swelling tendency of the gelatin layer can be observed directly when moistening the layer with water. The swelling tendency of the gelatin varies with the hardening degree. After the exposure a substantially unhardened gelatin layer will have regions which can be washed away completely by water at 25 C. and will provide transfer images of gelatin. After a similar exposure a layer of gelatin hardened in known way will show the increased swelling tendency only as a difference in the rate of swelling between the areas heated by the reflected light that is absorbed and those not, or negligibly, struck by reflected light. This may be illustrated by immersing the gelatin layer in an aqueous solution of a dye for only a few seconds, which results in a preferential absorption of the dye solution into the heated portions, thus producing a dye image.

According to several embodiments hectographic printing masters can be formed by using a gelatin relief image produced as described above.

According to one embodiment for producing a hectographic printing master a heat-sensitive gelatin layer is used which contains a water-insoluble or water-insolubilized hectographic dye or a colour reactant for forming a hectographic dye. Therefore, after the 'reflectographic exposure, the gelatin portions which are heated by the heat resulting from the reflected light that is absorbed are completely washed away by water having a temperature of 20 to 30 C. thus leaving a laterally reversed gelatin reliefimage. The material containing said image can be used as hectographic printing master.

According to another embodiment the material containing a laterally reversed gelatin relief, which is obtained after exposure and washing away the image-wise heated gelatin portions, is pressed with the gelatin relief against a hectographic carbon paper, e.g. as is used in the process according to the Canadian patent specification 666,600 and then after a few seconds peeled apart therefrom whereby a stratum of the dyestuff layer of the carbon paper is transferred to the laterally reversed gelatin relief image obtained. The material containing the transferred stratum of said dyestufl layer can be used as hectographic master.

According to still another embodiment a hectographic master for producing negative prints can be formed by transfer of the swollen gelatin portions to a receiving sheet. The said gelatin portions can be dyed before or after the transfer. The said transfer can be carried out by contacting under pressure a receiving sheet with the gelatin relief image, preferably between two rollers-at least one of which is preferably heated to a temperature between 30 and 50 C., and peeling apart both materials after emerging from the rollers.

For preparing a printing master wherein use is made of an image-wise lipophilic-hydrophilic differentiation as in a planographic printing master, a gelatin stratum of swollen gelatin or a gelatin stratum that remains after washing out the swollen portions can lac-transferred to a hydrophobic or hydrophilic lithographic support. As hydrophilic support may be used for instance a grained zinc, or aluminum or a casein-coated paper. In case a hydrophilic support is used the transferred gelatin has to be made hydrophobic.

The planographic printing master obtained can be used in conventional lithographic printing processes wherein use is made of a'lipophilicink and a damping system or aluminium sulphate, chrome alum, potash alum, formal- V 3 in the planographic printing process described in the Belgian patent specification 676,898 filed Feb. 23, 1966 by Gevaert-Agfa N.V. wherein use is made of a hydrophilic ink.

For preparing a screen printing master or stencil the swellable gelatin can be applied in or over the screen openings of a support suited for stencil preparation. As screening support Japan paper (Yoshino paper), nylon fabrics with a size of mesh of 0.2 to 0.08 mm. and woven bronze wire are specially suitable. The stencil can be prepared by washing out the image-wise heated gelatin portions. It is, however, also possible to prepare a stencil by image-wise transferring a stratum of moist and swollen gelatin to a screening material containing no coating; so image-wise filling up the screen-openings through which the stencil ink on printing may not penetrate.

The transfer'red gelatin may be hardened to improve the mechanical strength of the stencil. Various types of gelatin can be used for preparing the heat-sensitive recording material; so it has been found that gelatins with low Bloom gel strength value as well as gelatins with Bloom gel strength value above 200 are suitable for obtaining a practically useful image-differentiation as will be illustrated further on in the examples. Suitable gelating layers for application in the present invention are described in UK. patent specification 985,933 filed Apr. 14, 1961 by Kodak. The gelatin that is useful in the recording and reproduction method as described above includes derivatives of gelatin such as those described in Belgian patent specification 484,324 filed Aug. 26, 1948 by Kodak, Belgian patent specification 606,122 filed July 14, 1961 by Gevaert Photo-Producten N.V. and in Belgian patent specification 609,566 filed Sept. 27, 1961 by Gevaert Photo-Producten N.V.

When from one matrix more than one gelatin relief transfer image has to be formed it is preferred to use a substantially unhardened gelatin and to carry out the transfer in the presence of a gelatin tanning agent e.'g.

dehyde, chromium chloride, glyoxal and tannic acid which hardening agents are generally incorporated in the aqueous moistening bath. This enables a large number of transfer copies to be obtained.

According to a special embodiment a gelatin layer is used that has been hardened with a metal salt e.g. aluminium sulphate which is removed afterwards whereby an runhardened gelatin is left. In this case, the gelatin -is preferably unhardened by a treatment with a complexing agent for the meal ions of the hardener.

-Accordingly to this embodiment the complexing taining said" substances that absorb electromagnetic radiation and transform it into heat to a transparent support which practically does not conduct heat e.g. a cellulose triacet'ate support. The optical density of the gelatin layer in respect of the used copying light is preferably between 0.3 and 0.8.. In otherwords, preferably at least 20% and at most 80% of the copying light is transmitted through the recording material and-impinges onto the image-wise reflecting original. 1

" The gelatin layer is preferably mainly composed of gelatin" (it preferably consists of more than 80% by weigh't'of gelatin) but may contain to a certain degree substances in dissolved and/or dispersed state, with the proviso, however, that these substances do not or only slightly adversely aifect the desired swelling rate. So,

the gelatin layer may contain e.g. dyes, catalysts or reaction components for the formation of dyes, protective colloids for the applied dispersed substances, reducing agents, developing substances for silver halide, finely divided metal that can be etched, developing nuclei for complexed silver halide, light-sensitive substances, plasticizing agents, hygroscopic compounds e.g. glycerol, 1,5-hexanediol and magnesium chloride, and curing agents in latent form. The concentration of these ingredients in the thermo-sensitive layer or other layer or sheet forming part of the recording material may not be such that the heat-sensitive material becomes too opaque for refiectographic exposure.

As substances which absorb visible light and infra-red light and convert it into heat of conduction are preferably used: finely divided carbon black, graphite, prussian blue, oxides, sulphides or carbonates of heavy metals, particularly of those heavy metals having an atomic weight between 45 and 210, such as manganese or lead sulphide or these heavy metals themselves in finely divided state such as silver, bismuth, lead, iron, cobalt and nickel. The amount of pigment incorporated into in the recording layer is preferably such that an optical density of the layer of 0.20 to 0.80 is obtained.

For pigments which absorb visible light and convert it into heat also reference is made to Belgian patent specification 657,502 filed Dec. 23, 1964 by Agfa A.G. and to UK. patent application 20,818/65 filed May 17, 1965 by Gevaert-Agfa N.V. which latter application is deemed to be read in conjunction herewith.

According to a special embodiment the gelatin layer is, during the exposure, uniformly in heat-conductive relationship with coloured substances which absorb light of a determined part of the visible spectrum and convert it into heat. A gelatin layer spectrally sensitized in this way can be used for recording coloured originals in terms of differences in solubility and in swelling tendency in water.

More particulars about substances that absorb visible light and convert it into heat can be found in UK. patent application 21,985/ 65 filed May 24, 1965 by Gevaert- Agfa N.V. which is an addition to UK. patent application 20,818/ 65 filed May 17, 1965 by Gevaert-Agfa N.V. and such applications should be read in conjunction herewith.

It is to be understood that mixtures of said coloured substances can be used too, so that light of the whole visiblespectrum is absorbed. Further the said substances have not to absorb in the range of the visible spectrum alone, they may absorb in the infra-red region although for a good recording of red coloured image-markings the latter absorption is preferably as low as possible.

The coloured substances or mixture of said substances when used for optical sensitization of the gelatin layer preferably absorb light corresponding to at least one of the primary colours (red, green, blue) or subtractive solved state; when they are used in dispersed form they are preferably applied with a grain size lower than 0.1

According to the present invention, when using optically sensitized gelatin layers, it is possbile to produce printing masters suitable for colour printing and forproducing multicolour copies of colour originals. For that purpose three materials are usedv that contain a heat-sensitive gelatin layer comprising a substance which is heated on absorbing red, green and blue light respectively, i.e. a gelatin layer containing a cyan dye, a magenta dye and a yellow dye respectively. Said dyes may be dyes suitable for hectographic printing.

By the heat produced in the heat-sensitive gelatin layer containing the cyan dye said layer is made more swellable and water-dissolvable in the areas corresponding to the red areas of the original to which it was exposed.

By the heat produced in the heat-sensitive gelatin layer containing the magenta dye said layer is made more swellable and water-dissolvable in the areas corresponding to the green areas of the original to which it was exposed.

By the heat produced in the heat-sensitive gelatin layer containing the yellow dye said layer is made more swellable and water-dissolvable in the areas corresponding to the blue areas of the original to which it was exposed.

Multicolour prints can be produced by using the three exposed materials to prepare three separate masters which are used to print in register.

For reproducing originals that contain separate markings in the pure primary colours: blue, green and red (e.g. a letter heading containing blue, green and red letters), three separate gelatin layers can be used which are sensitized for blue, green and red respectively by a blue, green and red dye or pigment that is uniformly distributed therein. By washing away the selectively heated gelatin portions copies of the image markings in the primary colours are obtained.

The effectiveness of the recording with visible light substantially depends on the intensity of the radiant energy. For example, a gelatin recording layer, that does not provide a sufiicient differentation in swelling tendency with a particular source of electromagnetic radiation energy may be fully effective if the energy level is substantially increased.

Lamp structures and exposure systems producing electromagnetic radiation at least 70% of which consists of visible light (in other words containing only small amounts of U.V. light and infra-red light) and which are capable of providing high-intensity radiation in a very small lapse of time are preferably used.

10% aqueous dispersion of colloidal silver Radiation sources emitting visible 'lightof high intensity in a very small lapse of time are so-called flash lamps and more particularly the discharge lamps containing an inert gas. h p

In the present invention good results are obtained with a Xenon gas discharge lamp, which can supply an energy of 300-l000 watt. sec. in a time interval of 10* to 10"" seconds.

According to a preferred embodiment of the invention It is possible to employ a number of flash tubes operat-' ing simultaneously, or to obtain a suitable image-differentiation by flashing a single tube at suitable intervals. Reflectors and other optical components may be included to provide irradiation of maxium uniformity.

Evidently lamps with a lower energy output can be" used if the emitted light energy is focused onto a rela-.

tively small heat-sensitive area. So, e.g., a gas discharge lamp with an energy output of 40 watt see. is

suited for copying 6 cm. x 6 cm. and 6 cm. x 9 cm. originals on a heat-sensitive material as described in the present invention. It is further self-explanatory that exposure may be progressive and intermittentln other words the heat-sensitive material may be reflectographically scanned with an image-wise modulated light-spot of high intensity, e.g. a laser beam, or may be progressively exposed through a slit wherein, e.g., copying light of a continuously emitting tube-like radiation source is focused.

The specifications of the patents and patent applications hereinbefore referred to, which should be read in conjunction herewith are to be deemed to formpart of the present disclosure.

The present invention is illustrated by the following examples without, however, limiting it thereto.

In the first four working examples which follow, the gelatin layer is in contact with light-absorbing markings of the original during the exposure. Although the said markings are thus in some degree in heat-conductive relationship with the gelatin layer they do not or do not effectively heat the gelatin. A flash exposure is used, and during this exposure the only effective heating of the gelatin which occurs is due to the heating of the light-absorbing substance which is distributed in the gelatin layer. itself.

EXAMPLE 1 A poly(ethylene terephthalate) support of 0.1 mm. thickness provided with a subbing layer for gelatin is coated with the following composition pro rata of 50 g./sq. m.:

G. 10% aqueous solution of gelatin having a Bloom gel strength value of 240 450 10% aqueous saponin solution 15 20 tion-absorbing markings 22 and a radiation-reflecting background 23, the heat-sensitive gelatin layer 20 facing the original. The sandwich of copying material and original is then braced around a glass cylinder 24 having a diameter of 8 cm. The support 27, which carries the subbing layer 28 and the heat-sensitive layer 20, is contacting the outer wall of the glass cylinder 24. In the axis of this cylinder a Xenon gas discharge lamp 25 is placed, which at the discharge between the electrodes 26 produces a radiation energy of 610 watt sec. in sec. The applied radiation mainly consists of visible light.

After exposure the recording material is dipped in water of 20 C. and gently rubbed. The areas corresponding to the white background of the original are washed away, whereas the areas corresponding to the absorbing letter marks 22 do not dissolve.

The gelatin relief obtained is pressed a'gainst the dyestutf layer of a hectographic carbon carrying no hydrophobic surface layer.

After a contact time of about 30 sec. both layers are separated. At the areas corresponding with the latter marks of the original a stratum of the dyestutf layer is transferred to the gelatin relief image, so that a dyestulf containing laterally reversed relief image of the original is obtained.

This material can then be utilised as a spirit duplicating master.

EXAMPLE 2 A cellulose triacetate support of 0.12 mm. thickness provided with a subbing layer for gelatin is coated with the following composition pro rata of 30 g./sq.

10% aqueous solution of gelatin with Bloom gel strength 150 200 1% dispersion of carbon black in water 200 5% aqueous sdlution of sodium tetradecyl sul-f phate 10 Water '7 After having been dried, the Japan paper thus treated can be used as a stencil.

On the cellulose triacetate support a positive gelatin image remains which is legible through the back of said support.

EXAMPLE 3 A poly(ethylene terephthalate) support of 0.1 mm. thickness provided with a subbing layer for gelatin is coated with the following composition pro rata of 70 g. per sq. m.: G aqueous gelatin solution (the gelatin has a Bloom gel strength value of 140) 450 10% aqueous saponin solution 3% aqueous solution of the sodium salt of the condensation product of oleic acid and methyltaurine 15 Pigment griin B Pigmosol (C.I. 10.006) 10 Permanent Violett R.L. Colanyl Teig (C.I. 51.300)

(Hoechst) 10 8 Although as can be learned from the drawing (FIG. 2) the heat-sensitive layer stands in contact with the lightabsorbing markings of the original 31 there is insufficient heat-conductive relationship between said markings and the heat-sensitive layer.

After the recording material 28 is dipped in water of 20 C. and gently rubbed. Only the areas corresponding to the black and green letter marks of the original do not dissolve. The laterally reversed copy obtained in the form of a coloured gelatin relief image is pressed against a receiving paper and separated therefrom after five seconds.

A legible transfer copy of only the black and green letter marks of the original is obtained.

EXAMPLE 4 A poly(ethylene terephthalate) support of 0.1 mm. thickness provided with a subbing layer for gelatin is coated with the following solution pro rata of g. per

sq. m.:

Grams 20% aqueous solution of gelatin (the gelatin has a Bloom strength value of 200) 200 2% aqueous solution of: I 1

some. some 124 N o=o no-c N "mo-ii :=oH--ii%-om 7% aqueous solution of: v

I some 125 HZNQQC/ int S OaNa 5% aqueous solution of:

3 l $05K 35 Q I 1 I N nao-t i-o=on-on on'- on'=oHJi-iL-om Zi% a?1%e s;lfi2io rl of the sodium salt of the condensation product of oleic 10 W222? and methyltanrina The layer is dried whereupon the material obtained is exposed together with an original as described in Example 3. After exposure the material is dipped in water of 20 Cland the areas corresponding to the white background of' the original are washed away. The gelatin relief obtained is pressed against the dye layer of a hectographic carbon carrying no hydrophobic surface layer.

After a contact time of about 30 see. both layers are separated. At the areas corresponding with the image areas of the original a stratum of the dyestufl layer is transferred to the gelatin relief so that a dyestutf containing laterally reversed image of the original is obtained. This material can then be utilised as a spirit duplicating master.

EXAMPLE A poly(ethylene terephthalate) support of 0.14 mm. thickness provided with a subbing layer for gelatin is coated with the following composition pro rata of 50 g./sq./m.:

G. 10% aqueous solution of gelation having a Bloom gel strength value of 240 450 10% aqueous saponin solution 10% aqueous dispersion of colloidal silver 2 0 The layer is dried at C.

After drying the heat-sensitive copying material 32 comprising a poly(ethylene terephthalate) support 35, a gelatin subbing layer 34 and a heat-sensitive layer 33 is reflectographically exposed with a flash-lamp 27 to an opaque original 36 as diagrammatically illustrated in the accompanying FIG. 3.

After exposure the material is slightly wetted with water and then with its heat-sensitive layer pressed against a receiving paper. Material and receiving paper are led between two pressure rollers at a travelling speed of about 10 cm./sec., and peeled apart. A thin stratum. of the heatsensitive layer is transferred image-wise to the receiving paper. A hectographic carbon with its dyestuif layer carrying no hydrophobic surface layer is pressed against the receiving paper. After a contact time of about 1 min. both layers are separated. A dyestuff-containing laterally reversed image of the original is obtained on the receiving paper which can be used as a spirit duplicating master.

We claim:

1. A method of recording information, comprising the steps of providing a recording material including a recording layer, which consists of at least about 80% by weight of gelatin and contains homogeneously distributed therein a finely divided material that absorbs visible light and converts absorbed light into heat, said material being present in such an amount that at least 20% and at most 80% of the visible light to which the original is exposed is transmitted; reflectographically exposing the recording layer while in direct contact with an original having visible light-absorbing markings on a visible light-reflecting background for a time not longer than 10 seconds, said exposure being of such an intensity as to heat portions of said recording layer corresponding to said background to the extent that the swelling rate and the rate of dissolution in water of the gelatin are increased but not of such intensity as to heat portions of said recording layer corresponding to said light-absorbing markings to the extent that the swelling rate and the rate of dissolution in water of the gelatin are increased, and developing the image formed on the recording layer by swelling or dissolving the heated portions of the gelatin.

2. A method for recording information according to claim 1, wherein said material is a pigment.

3. A method for recording information according to claim 2, wherein said pigment is finely divided carbon particles.

4. A method for recording information according to claim 1, wherein said exposure is to a high-intensity discharge lamp containing an inert gas.

5. A method for recording information according to claim 1, wherein the exposed gelatin layer is moistened with water or an aqueous composition whereby the gelatin in the areas struck by reflected light is caused to swell.

6. A method for recording information according to claim 5, wherein a stratum of the swollen gelatin areas is transferred to a receiving sheet by pressing the recording layer containing said swollen gelatin areas against said sheet and subsequently peeling said layer apart therefrom.

7. A method for recording information according to claim 5, wherein swollen gelatin in the areas heated by reflected light is washed away.

8. A method for recording information according to claim 6, wherein the transferred gelatin stratum is dyed with a hecto graphic dye.

9. A method for recording information according to claim 5, wherein the swollen gelatin areas are washed away and the recording layer with the remaining gelatin relief is pressed against a dye layer of a hectographic carbon which is not coated with a hydrophobic protective layer and peeled apart therefrom thus transferring a stratum of said dye layer in correspondence with said relief image to said relief image.

10. A method for recording information according to claim 5, wherein the swollen gelatin areas are washed away and the recording layer with the remaining gelatin relief image is pressed against a screening element as used for preparing a screen printing master whereby gelatin,

in correspondence with the relief image, is transferred in the screen openings thereof.

11. A method for recording information according to claim 1, wherein the gelatin layer is applied to a support which is transparent for visible light.

I12. A method for recording information according to claim 1, wherein said substances absorb light of a determined part of the visible spectrum and transform it into heat.

13. A method for recording information according to claim 12, wherein said substances mainly absorbs in the range of one of the primary or subtractive colours.

14. A method for recording information according to claim 1, wherein the refiectographic exposure occurs to a transparent original, which during the exposure is held with its back side in contact or in proximity of a visible light reflecting material.

References Cited UNITED STATES PATENTS 3,121,162 2/1964 Roman et a1 1l71.7 X 3,298,833 11/1967 Gaynor 96-27 GEORGE F. LESMES, Primary Examiner R. E. MARTIN, Assistant Examiner US. Cl. X.R.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 523 791 Dated August 11, 1970 Invent0r(s) Marcel Nicolas VRANCKEN et al It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 3, line 33, change "609,566" to 608,566

Column 5, line 50, change "664,858" to 664,868

Column 6, line 50, change "latter" to letter sluiazn'mu SEALER nmzom n, H Luau I, M

MIMI!" rm; m

Gomlssiom of Patents FORM POJOSO (10-69) USCOMM-DC GOSIO-POO 

1. A METHOD OF RECORDING INFORMATION, COMPRISING THE STEPS OF PROVIDING A RECORDING MATERIAL INCLUDING A RECORDING LAYER, WHICH CONSISTS OF AT LEAST ABOUT 80% BY WEIGHT OF GELATIN AND CONTAINS HOMOGENEOUSLY DISTRIBUTED THEREIN A FINELY DIVIDED MATERIAL THAT ABSORBS VISIBLE LIGHT AND CONVERTS ABSORBED LIGHT INTO HEAT, SAID MATERIAL BEING PRESENT IN SUCH AN AMOUNT THAT AT LEAST 20% AND AT MOST 80% OF THE VISIBLE LIGHT TO WHICH THE ORIGINAL IS EXPOSED IS TRANSMITTED; REFLECTOGRAPHICALLY EXPOSING THE RECORDING LAYER WHILE IN DIRECT CONTACT WITH AN ORIGINAL HAVING VISIBLE LIGHT-ABSORBING MARKINGS ON A VISIBLE LIGHT-REFLECTING BACKGROUND FOR A TIME NOT LONGER THAN 10**1 SECONDS, SAID EXPOSURE BEING OF SUCH AN INTENSITY AS TO HEAT PORTIONS OF SAID RECORDING LAYER CORRESPONDING TO SAID BACKGROUND TO THE EXTENT THAT THE SWELLING RATE AND THE RATE OF DISSOLUTION IN WATER OF THE GELATIN ARE INCREASED BUT NOT OF SUCH INTENSITY AS TO HEAT PORTIONS OF SAID RECORDING LAYER CORRESPONDING TO SAID LIGHT-ABSORBING MARKINGS TO THE EXTENT THAT THE SWELLING RATE AND THE RATE OF DISSOLUTION IN WATER OF THE GELATIN ARE INCREASED, AND DEVELOPING THE IMAGE FORMED ON THE RECORDING LAYER BY SWELLING OR DISSOLVING THE HEATED PORTIONS OF THE GELATIN. 